Heat exchangers are used for transferring heat in a variety of systems such as those for manufacturing, heating ventilating and air-conditioning, power generation, and electronic packaging. One goal in the design of a heat exchanger is to maximize the convective heat transfer between a working fluid and a solid wall. One way to do this is by increasing the velocity of the fluid, which enhances the wall convective heat transfer coefficient. However, as per the estimates of Kays and London (1984), while the heat transfer coefficient is directly proportional to the velocity, the power required to drive the flow is proportional to the square of the velocity. This imposes an upper limit on the maximum allowable velocities in the heat exchanger.
Most compact heat exchangers employ closely spaced fins or similar structures to augment the heat transfer area for a given device volume. Additional augmentation requires modifying the wall boundary layer flow, usually with the help of turbulence promoters, such as baffles or wall roughness elements. This is generally necessary for heat exchange from air streams due to significantly lower heat capacities and thermal conductivities of air compared to water or other commonly used liquid heat transfer media.
The principal problem of this solution is that using such turbulence promoters causes a significant drop in flow pressure, thereby increasing the power consumption of the fans. A second drawback is that turbulence promoters often snag solid particles or debris, thereby increasing flow blockage and heat transfer surface fouling in many instances.
Generally, there is not a good solution to these problems. Accordingly, what is needed is a system and method for increasing heat transfer while minimizing, or eliminating the additional flow pressure drop. The present invention addresses such a need.